1. Field of the Invention
The present invention relates to a process of manufacturing a fiber reinforced plastic armored cable for communications or power uses which has a peripheral surface protected and reinforced by fiber reinforced plastic rod-like members or strands.
2. Description of the Prior Art
It is well-known in the art that a cable for communications or power uses is armored with fiber reinforced plastic strands for protecting and reinforcing it. A typical example of such a cable is a large capacity optical fiber cable for communication. The optical fiber cable of this kind has an optical fiber carrying spacer formed of high density polyethylene or similar thermoplastic resin about a tension member and having a plurality of helical grooves cut in its peripheral surface. An optical fiber or tape-like optical fiber core formed by a plurality of optical fibers arranged flat in side-by-side relation is inserted into each helical groove of the spacer and then the spacer thus carrying the optical fibers is coated over the entire area of its peripheral surface with a thermoplastic resin. The optical fiber carrying spacer is disclosed in detail in U.S. Pat. No. 4,781,434. The optical fiber cable thus obtained is usually armored with high-tensile rod-like members so that it is protected from lateral pressure, tensile force and other external forces.
In the case of armoring the optical fiber cable or similar cable, if fiber reinforced plastic strands obtained by curing thermosetting resin impregnated into reinforcing fibers are wound around the cable, there is the possibility of stress cracking in the strands because of high rigidity of the fiber reinforced plastic material. To avoid this problem, there has been proposed an armored cable manufacturing process in which strands of uncured or semi-cured resin are wound around the cable, as set forth in Japanese Patent Publication No. 50364/81.
In the above-mentioned Japanese Publication there is also disclosed an example of such an uncured armoring strand formed by coating an uncured or semi-cured fiber reinforced plastic rod-like member with a protective layer for preventing the adhesion thereto of foreign material.
On the other hand, a composite fiber reinforced plastic strand suitable for use as the above-noted uncured armoring strand is set forth in U.S. Pat. No. 3,946,097 owned by the assignee of this application. The strand is obtained by impregnating reinforcing fibers with an uncured thermosetting resin, coating the resin-impregnated reinforcing fibers with a thermoplastic resin and then solidifying the coated thermoplastic resin while maintaining the internal thermosetting resin uncured.
In the case of employing the above composite fiber reinforced plastic strand for armoring a cable, however, conventional separate steps of producing the uncured strands and armoring the cable therewith impair the storage stability of the uncured thermosetting resin and degrade the physical properties of the composite fiber reinforced plastic strands. This is attributable to an offset or disorder of the arrangement of the reinforcing fibers in the step of winding them on a drum or bobbin.
In Japanese Patent Publication No. 139872/89 filed in the name of the assignee of this application there is disclosed a special thermosetting resin composition of a long pot life for improving the storage stability of the uncured thermosetting resin. However, a fiber reinforced plastic strand formed of the resin of the composition proposed in the above-noted Japanese Publication also suffers lowered strength which is caused by aging of the resin, and its strength after curing may sometimes be inferior to that in the case where a thermosetting resin of a typical composition containing a styrene monomer as a crosslinking component is used and is cured immediately after being impregnated into fibers. Moreover, the problem of offset or disorder of the arrangement of the reinforcing fibers still remains unsolved.
In the fabrication of optical fiber cables, in particular, it is necessary to insert optical fibers into helical grooves of the spacer. This calls for rotating the optical fibers wound on bobbins or the like, or rotating the spacer about its longitudinal axis. In this instance, however, the facility for rotating the bobbins inevitably becomes larger in size with an increase in the length of the cable. In addition, in the case of armoring the thus obtained cable with the fiber reinforced plastic strands, it is necessary to rotate the drum with the strands wound thereon or the cable itself. At any rate, the strands which are long and wound on the drum must be supplied therefrom, and the conventional manufacturing method inevitably necessitates the use of complicated and bulky apparatus.